US6220309B1

US6220309B1 - Inflatable fabrics comprising basket-woven attachment points between fabric panels

Info

Publication number: US6220309B1
Application number: US09/406,264
Authority: US
Inventors: John A. Sollars, Jr.
Original assignee: Milliken and Co
Current assignee: Milliken and Co
Priority date: 1999-09-24
Filing date: 1999-09-24
Publication date: 2001-04-24
Anticipated expiration: 2019-09-24
Also published as: BR0014270A; WO2001021870A1; US7543609B2; CN100441757C; US20080302438A1; EP1268900A4; CA2385556A1; EP1268900B1; JP2003510469A; JP5265960B2; US7069961B2; EP1268900A1; JP4256093B2; US20060249933A1; US7409970B2; EP1921186A1; US6595244B1; CN1376219A; US20030188797A1; DE60038701D1

Abstract

An all-woven inflatable fabric having areas of two layers and attachment points or “seams” where single layers of fabric are formed. Such single fabric layers are constructed solely through the utilization of basket weave patterns. These specific single fabric layers provide a relatively effective manner of reducing air permeability within the entire fabric article by decreasing the possibility of yarn shifting upon inflation of the inflatable fabric. Alternatively, the presence of at least a second single fabric layer area adjacent to the first and separated by a narrow double fabric layer can further reduce the possibility of yarn shifting in the first single fabric layer area. Such a fabric may be utilized in numerous and various applications wherein fabric inflation is desired or necessary. In particular, the inventive fabric may be incorporated within an airbag cushion.

Description

FIELD OF THE INVENTION

The invention relates to all-woven inflatable fabrics which comprise areas of two layers and attachment points or “seams” where single layers of fabric are formed. Such single fabric layers are constructed solely through the utilization of basket weave patterns. These specific single fabric layers provide a relatively effective manner of reducing air permeability within the entire fabric article by decreasing the possibility of yarn shifting upon inflation of the inflatable fabric. Alternatively, the presence of at least a second single fabric layer area adjacent to the first and separated by a narrow double fabric layer can further reduce the possibility of yarn shifting in the first single fabric layer area. Such a fabric may be utilized in numerous and various applications wherein fabric inflation is desired or necessary. In particular, the inventive fabric may be incorporated within an airbag cushion.

BACKGROUND OF THE PRIOR ART

All U.S. patent cited herein are hereby fully incorporated by reference.

Inflatable protective cushions used in passenger vehicles are a component of relatively complex passive restraint systems. The main elements of these systems are: an impact sensing system, an ignition system, a propellant material, an attachment device, a system enclosure, and an inflatable protective cushion. Upon sensing an impact, the propellant is ignited causing an explosive release of gases filing the cushion to a deployed state which can absorb the impact of the forward movement of a body and dissipate its energy by means of rapid venting of the gas. The entire sequence of events occurs within about 30 milliseconds. In the undeployed state, the cushion is stored in or near the steering column, the dashboard, in a door, or in the back of a front seat placing the cushion in close proximity to the person or object it is to protect.

Inflatable cushion systems commonly referred to as air bag systems have been used in the past to protect both the operator of the vehicle and passengers. Systems for the protection of the vehicle operator have typically been mounted in the steering column of the vehicle and have utilized cushion constructions directly deployable towards the driver. These driver-side cushions are typically of a relatively simple configuration in that they function over a fairly small well-defined area between the driver and the steering column. One such configuration is disclosed in U.S. Pat. No. 5,533,755 to Nelsen et al., issued Jul. 9, 1996, the teachings of which are incorporated herein by reference.

Inflatable cushions for use in the protection of passengers against frontal or side impacts must generally have a more complex configuration since the position of a vehicle passenger may not be well defined and greater distance may exist between the passenger and the surface of the vehicle against which that passenger might be thrown in the event of a collision. Prior cushions for use in such environments are disclosed in U.S. Pat. No. 5,520,41 to Bishop; U.S. Pat. No. 5,454,594 to Krickl; U.S. Pat. No. 5,423,273 to Hawthorn et al.; U.S. Pat. No. 5,316,337 to Yamaji et al.; U.S. Pat. No. 5,310,216 to Wehner et al.; U.S. Pat. No. 5,090,729 to Watanabe; U.S. Pat. No. 5,087,071 to Wallner et al.; U.S. Pat. No. 4,944,529 to Backhaus; and U.S. Pat. No. 3,792,873 to Buchner et al.

The majority of commercially used restraint cushions are formed of woven fabric materials utilizing multifilament synthetic yarns of materials such as polyester, nylon 6 or nylon 6,6 polymers. Representative fabrics for such use are disclosed in U.S. Pat. No. 4,921,735 to Bloch; U.S. Pat. No. 5,093,163 to Krummheuer et al.; U.S. Pat. No. 5,110,666 to Menzel et al.; U.S. Pat. No. 5,236,775 to Swoboda et al.; U.S. Pat. No. 5,277,230 to Sollars, Jr.; U.S. Pat. No. 5,356,680 to Krummheuer et al.; U.S. Pat. No. 5,477,890 to Krummheuer et al.; U.S. Pat. No. 5,508,073 to Krummheuer et al.; U.S. Pat. No. 5,503,197 to Bower et al., and U.S. Pat. No. 5,704,402 to Bowen et al. A two-weave construction airbag cushion is exemplified in U.S. Pat. No. 5,651,395 to Graham et al. but does not discuss the importance of narrow basket-weave single fabric layers.

As will be appreciated, the permeability of an airbag cushion structure is an important factor in determining the rate of inflation and subsequent rapid deflation following the impact event. Different airbag cushions are utilized for different purposes. For instance, some airbag cushions are installed within inflation modules for driver protection within the steering column of an automobile. Others are utilized as protection for front seat passengers and are installed in and around the glove compartment and/or on the dashboard in front of such a passenger seat. Still others have been developed in an effort to protect all passengers during a long-duration impact event, such as, for example, a rollover collision. In those types of crashes, the target airbag cushion must inflate quickly under high pressure (such as between about 10 and 40 psi) and remain inflated at a relatively high pressures in order to provide the greatest degree of protection to such passengers. Furthermore, such long-duration airbag cushions preferably comprise “pillow” formations created through the attachment of at least two different fabrics or fabric ends together and sealed, sewn, or the like, together. Upon inflation the free space between the attachment points inflate as well, thereby producing the desired cushioned “pillow” structures. Such long-duration, “pillowed” structures have been disclosed in the prior art as airbag cushions within U.S. Pat. No. 5,788,270 to Halano. However, in order to provide a suitable, effective airbag fabric and cushion comprising two or more points of attachment between fabrics or fabric ends, there has been a need to improve upon the structural integrity of the seams at such attachment points to prevent unwanted and potentially harmful leakage of gas or air from within the target airbag cushion. The prior art has discussed the development of coatings to place over the sewn seams at such attachment points in order to seal the potentially loose portions of such seams and/or to keep the individual yarns of the airbag fabrics at the attachment points stationary in order to prevent yarn shifting and thus possible openings for air or gas leakage. However, such coatings are actually supplemental to the seam structures in providing the necessary barrier to air or gas. A strong, effective, efficient weave construction is the primary method of initially producing an effective airbag fabric for incorporation within an airbag cushion.

Previous attempts have been made at producing inflatable fabrics comprising “pillowed” chambers (such as for side curtains, and the like) which have been produced solely through a weaving procedure and which exhibit reduced air permeability within their weave constructions (in other words, fabrics which are not sewn together to form an inflatable structure). For instance, the closest art appears to be U.S. Pat. 5,011,183 to Thornton et al. which discloses an inflatable fabric structure comprising at least two different areas of differing fabric layers. Patentees discuss two layers of fabric produced by a plain weave and single layer constructions of a plurality of different weave patterns. The interface between the two different fabric layer areas must exhibit at least three different fabric densities (which are dictated by weave constructions), wherein the two looser constructions (double layer plain weave and single layer basket weave) are separated by a tighter construction (single layer plain weave). Such an overall inflatable fabric structure may possess the necessary air permeability characteristics required for proper functioning within a side curtain airbag cushion (particularly upon coating with a standard airbag coating composition); however, the numerous differences in fabric densities also place varying pressures upon discrete areas of the fabric (particularly at or near the interface between the differing fabric layer areas) such that yarn shifting will most likely occur during an inflation event which may produce discontinuities in the integrity of the coating which may in turn compromise the long-term air permeability required for certain airbag applications.

Attempts have been made at improving on such a fabric; however these have led to an increase in the number of different fabric density areas on the fabric, rather than reducing such differing densities. For example, a plain weave construction has been utilized within the double layer area, adjacent to a transition weave pattern, which connects with an Oxford weave pattern, and then either a basket-weave or plain weave construction for the remainder of the single layer area on the fabric. Such a complicated scheme is difficult to produce on a weaving apparatus, as an initial problem. Secondly, the utilization of an Oxford weave zone has been utilized in an attempt to prevent the possibility of weaving in a plain pattern (which is highly undesirable due to the difficulty in manufacturing such high density single-layers fabrics from double-layer amounts of yarn). However, if the area of single layer of fabric is not substantially a straight line, and thus must follow a curved structure, the Oxford weave will eventually become a plain weave for at least that area around such a curved seam. In such an instance, the interface between the two differing layers of fabric will be irregular and invariably produce an undesirable and/or irregular number of floats (i.e., yarns which pass either over or under a certain number of perpendicularly oriented yarns; greater than three such oriented yarns would produce difficulties in preventing yarn shifting, as merely one example). As such, the resultant fabric is itself highly undesirable as a barrier to air permeability, even though coatings may be applied to increase such performance. Thirdly, the individual yarns at the seam between the double and single layer areas, will be placed upon tremendous strain during an inflation event and, as in the Thornton et al. teaching, will most likely result in yarn shifting. With such shifting yarns, the permeability benefits, if any, would, again, most likely be compromised and the produced airbag fabric would not function as required.

To date, there has been no method or fabric structure which has remedied these problems and still can be efficiently woven in a one-step process. A clear need for such an improvement in inflatable fabrics is thus necessary.

SUMMARY OF THE INVENTION

In view of the foregoing, it is a general object of the present invention to provide an inflatable all-woven fabric having all-basket-woven seams at the single/double layer interfaces within the fabric. It is a more particular object of the present invention to provide an all-woven inflatable fabric with double layer zones of fabric and single layer zones of fabric (to form “pillowed” chambers) which comprises at most two different fabric densities throughout the entire fabric structure. Also, an object of this invention is for the utilization of such inflatable fabrics as airbag cushions within a vehicle restraint system. The term “vehicle restraint system” is intended to mean both inflatable occupant restraining cushion and the mechanical and chemical components (such as the inflation means, ignition means, propellant, and the like).

To achieve these and other objects and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides an inflatable fabric comprising at least two layers of fabric in certain discrete areas of the fabric and at least one narrow single fabric layer at a discrete area within said fabric, wherein said at least one narrow single fabric layer is formed solely from a basket weave pattern of an even number of yarns, at most 12 yarns in width; preferably, and as well known to the skilled artisan in the fabric weaving industry, the weave structure for said single layer fabrics is a 2×2 basket weave pattern at most from 4 to 8 yarns in length. Also, this invention encompasses an inflatable fabric comprising at least two layers of fabric in certain discrete areas of the fabric and at least one single fabric layer at a discrete area within said fabric, wherein the weave diagram for such a fabric does not exhibit more than three consecutive unfilled blocks in any row or column. Furthermore, this invention also concerns an inflatable fabric comprising at least two layers of fabric in certain discrete areas of the fabric and at least one single fabric layer at a discrete area within said fabric, wherein only two separate weave densities are present within the entire fabric structure.

The term “inflatable fabric” is intended to encompass any fabric which is constructed of at least two layers of fabric which can be sealed to form a bag article. The inventive inflatable fabric thus must include double layers of fabric to permit such inflation, as well as single layers of fabric either to act as a seal at the ends of such fabric panels, or to provide “pillowed” chambers within the target fabric upon inflation. The term “all-woven” as it pertains to the inventive fabric thus requires that the inflatable fabric having double and single layers of fabric be produced solely upon a loom. Any type of loom may be utilized for this purpose, such as water-jet, air-jet, rapier, dobby, and the like. Jacquard weaving and dobby weaving, however, are most preferred.

The constructed fabric may exhibit balanced or unbalanced pick/end counts; the main requirement in the woven construction is that the single layer areas of the inflatable fabric exhibit solely basket-weave patterns. These patterns are made through the arrangement of at least one warp yarn (or weft yarn) configured around the same side of two adjacent weft yarns (or warp yarns) within the weave pattern. The resultant pattern appears as a “basket” upon the arrangement of the same warp (or weft) yarn to the opposite side of the next adjacent weft (or warp) yarn. Such basket weave patterns may include the arrangement of a warp (or weft) yarn around the same side of any even number of weft (or warp) yarns, preferably up to about six at any one time.

The sole utilization of such basket weave patterns in the single layer zones provides a number of heretofore unexplored benefits within inflatable fabric structures. For example, such basket weave patterns permit a constant “seam” width and weave construction over an entire single layer area, even where the area is curved. As noted above, the standard Oxford weaves currently utilized cannot remain as the same weave pattern around curved seams; they become plain weave patterns. Also, such basket weave seam patterns permit the construction of an inflatable fabric having only plain woven double layer fabric areas and single layer “seams” with no “floats” of greater than three picks within the entire fabric structure. Such a fabric would thus not possess discrete locations where the air permeability is substantially greater than the remaining portions of the fabric. Generally, the prior art (such as Thornton et al., supra) produce floats of sometimes as much as six or seven picks at a time. Although available software to the weaving industry permits “filling in” of such floats within weave diagrams, such a procedure takes time and still does not continuously provide a fabric exhibiting substantially balanced air permeability characteristics over the entire structure. The basket-weave formations within the single fabric layers thus must be positioned in the fabric so as to prevent irregularities (large numbers of floats, for example) in the weave construction at the interface between the single and double fabric layers (as described in FIG. 2, below). Another benefit such basket weave patterns accord the user is the ability to produce more than one area of single layer fabric (i.e., another “seam” within the fabric) adjacent to the first “seam.” Such a second seam provides a manner of dissipating the pressure from or transferring the load upon each individual yarn within both seams. Such a benefit thus reduces the chances of deleterious yarn shifting during an inflation event through the utilization of strictly a woven fabric construction (i.e., not necessarily relying upon the utilization of a coating as well). The previously disclosed or utilized inflatable fabrics having both double and single fabric layer areas have not explored such a possibility in utilizing two basket-weave pattern seams. Furthermore, such a two-seam construction eliminates the need for weaving a large single fabric layer area within the target inflatable fabric. The prior art fabrics which produce “pillowed” chambers for airbag cushions (such as side curtains), have been formed through the weaving of entire areas of single fabric layers (which are not actually seams themselves). Such a procedure is time-consuming and rather difficult to perform. The inventive inflatable fabric merely requires, this alternative embodiment, at least two very narrow single fabric layer areas (seams) woven into the fabric structure (another preferred embodiment utilizes merely one seam of single layer fabric); the remainder of the fabric located within these two areas may be double layer if desired. Thus, the inventive fabric permits an improved, cost-effective, method of making a “pillowed” inflatable fabric.

The inflatable fabric itself is preferably produced from all-synthetic fibers, such as polyesters and polyamides, although natural fibers may also be utilized in certain circumstances. Preferably the fabric is constructed of nylon-6,6. The individual yarns utilized within the fabric substrate must generally possess deniers within the range of from about 40 to about 840; preferably from about 100 to about 630.

As noted above, coatings should be applied to the surface as a necessary supplement to the air permeability of the inventive fabric. Since one preferred ultimate use of this inventive fabric is as a side curtain airbag which must maintain a very low degree of air permeability throughout a collision event (such as a rollover where the curtain must protect passengers for an appreciable amount of time), a decrease in permitted air permeability is highly desirable. Any standard coating, such as a silicone, polyurethane, polyamide, polyester, rubber (such as neoprene, for example), and the like, may be utilized for this purpose and may be applied in any standard method and in any standard amount on the fabric surface.

Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice for the invention. It is to be understood that both the foregoing general description and the following detailed description of preferred embodiments are exemplary and explanatory only, and are not to be viewed as in any way restricting the scope of the invention as set forth in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several potentially preferred embodiments of the invention and together with the description serve to explain the principles of the invention wherein:

FIG. 1 is a cross-sectional view of an inventive all-woven inflatable fabric showing the preferred double and single layer areas including two separate single layer areas.

FIG. 2 is a weave diagram illustrating a potentially preferred repeating pick pattern formed using repeating plain weave and basket weave four-pick arrangements.

DETAILED DESCRIPTION OF THE DRAWINGS

Turning now to the drawings, in FIG. 1 there is shown a cross-section of a preferred structure for the double fabric layers 12, 14, 18, 20, 24, 26 and single fabric layers 16, 22 of the inventive inflatable fabric 10. Weft yarns 28 are present in each of these

fabric layer areas

12, 14, 16, 18, 20, 22, 24, 26 over and under which

individual warp yarns

38, 40, 42, 44 have been woven. The double fabric layers 12, 14, 18, 20, 24, 26 are woven in plain weave patterns. The single fabric layers 16, 22 are woven in basket weave patterns. Four weft yarns each are configured through each repeating basket weave pattern within this preferred structure; however, anywhere from two to twelve weft yarns may be utilized within these single fabric layer areas (seams) 16, 22. The intermediate double

fabric layer areas

18, 20 comprise each only four weft yarns 28 within plain weave patterns. The number of such intermediate weft yarns 28 between the single

fabric layer areas

16, 22 must be in multiples of two to provide the maximum pressure bearing benefits within the two

seams

16, 22 and thus the lowest possibility of yarn shifting during inflation at the interfaces of the

seams

16, 22 with the double

fabric layer areas

12, 14, 24, 26.

FIG. 2 shows the weave diagram 30 for an inventive fabric which comprises two irregularly shapes concentric circles as the seams. Such a diagram also provides a general explanation as to the necessary selection criteria of placement of basket-weave patterns within the fabric itself. Three different types of patterns are noted on the diagram by different shades. The first 32 indicates the repeated plain weave pattern throughout the double fabric layers (12, 14, 18, 20, 24, 26 of FIG. 1, for example) which must always initiate at a location in the warp direction of 4X+1, with X representing the number of pick arrangement within the diagram, and at a location in the fill direction of 4X+1 (thus, the pick arrangement including the specific two-layer plain-weave-signifying-block 32 begins at the block four spaces below it in both directions). The second 34 indicates an “up-down” basket weave pattern wherein an empty block must exist and always initiate the basket-weave pattern at a location in the warp direction of 4X+1, with X representing the number of repeating pick arrangements within the diagram, and at a location in the fill direction of 4X+1, when a seam (such as 16 and 22 in FIG. 1) is desired (thus, the pattern including the pertinent signifying “up-down” block 34 includes an empty block within the basket-weave pick arrangement in both the warp and fill directions four spaces below it). The remaining pattern, which is basically a “down-up” basket weave pattern to a single fabric layer (such as 16 and 22 in FIG. 1) is indicated by a specifically shaded block 36. Such a pattern must always initiate at a location in the warp direction of 4X+1 and fill of 4X+3, or warp of 4X+3 and fill of 4X+1, when a seam is desired. Such a specific arrangement of differing “updown” basket weave 34 and “down-up” basket weave 36 pattern is necessary to effectuate the continuous and repeated weave construction wherein no more than three floats (i.e., empty blocks) are present simultaneously within the target fabric structure. Furthermore, again, it is believed that there has been no such disclosure or exploration of such a concept within the inflatable fabric art.

While specific embodiments of the invention have been illustrated and described, it is to be understood that the invention is not limited thereto, since modifications may certainly be made and other embodiments of the principals of this invention will no doubt occur to those skilled in the art. Such modifications include, but are in no way limited to, the ability to produce reverse, mirror, or offset versions of the aforementioned two-pattern combinations within the inventive fabrics. Therefore, it is contemplated by the appended claims to cover any such modifications and other embodiments as incorporate the features of this invention which in the true spirit and scope of the claims hereto.

Claims

What I claim is:

1. An inflatable fabric comprising at least two layers of fabric in certain discrete areas of the fabric and at least two discrete narrow areas of single fabric layer at discrete areas within said fabric, wherein said at least two narrow areas of single fabric layer are each formed solely from a basket weave pattern of an even number of yarns, at most 12 yarns in width, wherein said at least two narrow areas of single fabric layers are separated by an area of at least two layers of fabric, and wherein the lengths of each single layer is from 4 to 8 yarns in length, wherein said at least two single fabric layer areas are seams through the inflatable fabric which run parallel to each other, and wherein said separator area of two layers of fabric between said two single layers of fabric comprises an even number of weft yarns.

2. The fabric of claim 1 wherein said separator area of two layers of fabric comprises at most 12 weft yarns and at least 2 weft yarns.

3. The fabric of claim 2 wherein said at least two single fabric layers are constructed solely from two-by-two basket weave patterns and said separator area of two layers of fabric comprises four weft yarns.

4. An inflatable fabric comprising at least two layers of fabric in certain discrete areas of the fabric and at least two discrete narrow areas of single fabric layer at discrete areas within said fabric wherein said at least two narrow areas of single fabric layer are each formed solely from a basket weave pattern of an even number of yarns, at most 12 yarns in width, wherein said at least two areas of single fabric layers are separated by an area of at least two layers of fabric, wherein the lengths of each single layer is from 4 to 8 yarns in length, and wherein a weave diagram having rows and columns of filled and unfilled blocks for the fabric does not exhibit more than three consecutive unfilled blocks in any row or column.

5. An inflatable fabric comprising at least two layers of fabric in certain discrete areas of the fabric and at least two discrete narrow areas of single fabric layer at discrete areas within said fabric, wherein said at least two narrow areas of single fabric layer are each formed solely from a basket weave pattern of an even number of yarns, at most 12 yarns in width, wherein said at least two areas of single fabric layers are separated by an area of at least two layers of fabric, wherein the lengths of each single layer is from 4 to 8 yarns in length, and wherein at least a portion of one of said at least two discrete narrow areas of single fabric layer form at least one of a non-linear seam and seal.

6. An inflatable fabric comprising at least two layers of fabric in certain discrete areas of the fabric and at least two discrete narrow areas of single fabric layer at discrete areas within said fabric, wherein said at least two narrow areas of single fabric layer are each formed solely from a basket weave pattern of an even number of yarns, at most 12 yarns in width, wherein said at least two areas of single fabric layers are separated by an area of at least two layers of fabric, wherein the lengths of each single layer is from 4 to 8 yarns in length, and wherein said fabric has three different types of patterns, the first pattern is a repeated plain weave pattern throughout at least two layers of fabric which must always initiate at a location in the warp direction of 4X+1, with X representing the number of pick arrangement a weave diagram, and at a location in the fill direction of 4X+1, pick arrangement including the specific two layer plain-weave-signifying-block begins at the block four spaces below it in both directions, the second pattern is an “up-down” basket weave pattern wherein an empty block must exist and always initiate the basket-weave pattern at a location in the warp direction of 4X+1, with X representing the number of repeating pick arrangements within the diagram, and at a location in the fill direction of 4X+1, when a single layer fabric is desired, the pattern including the pertinent signifying “up-down” block includes an empty block within the basket-weave pick arrangement in both the warp and fill directions four spaces below it, the third pattern is basically a “down-up” basket weave pattern to a single fabric layer and must always initiate at a location in the warp direction of 4X+1 and fill of 4X+3, or warp of 4X+3 and fill of 4X+1, when a seam is desired, such a specific arrangement of differing “up-down” basket weave and “down-up” basket weave pattern is necessary to effectuate the continuous and repeated weave construction wherein no more than three floats or empty blocks are present simultaneously within the target fabric structure.

7. An inflatable fabric comprising at least two layers of fabric in certain discrete areas of the fabric and at least two discrete narrow areas of single fabric layer at discrete areas within said fabric, wherein said at least two narrow areas of single fabric layer are each formed solely from a basket weave pattern of an even number of yarns, at most 12 yarns in width, wherein said at least two areas of single fabric layers are separated by an area of at least two layers of fabric, wherein the lengths of each single layer is from 4 to 8 yarns in length, and wherein weft yarns are present in each of the fabric layer areas over and under which individual warp yarns have been woven, the at least two layer fabric areas are woven in plain weave patterns, the single fabric layer areas are woven in basket weave patterns, four weft yarns each are configured through each repeating basket weave pattern, however, anywhere from two to twelve weft yarns may be utilized within the single layer fabric areas or, the intermediate two layer fabric areas comprise each only four weft yarns within plain weave patterns, the number of such intermediate weft yarns between the single layer fabric areas must be in multiples of two to provide the maximum pressure bearing benefits within the two seams with the at least two layer fabric areas.